As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
A number of different connection protocols have been developed and used for connecting devices together, including the connection of displays to information handling systems. One such connection protocol is described in the DisplayPort Standard (Version 1.1) and in the Errata for the DisplayPort Standard (Version 1.1), which are each hereby incorporated by reference in its entirety. As stated therein, the DisplayPort Standard (DP Standard) and DP Standard Errata (Errata) specify an open digital communications interface for use in both internal connections, such as interfaces within a PC or monitor, and external display connections, including interfaces between a PC and monitor or projector, between a PC and TV, or between a device such as a DVD player and TV display. The purpose of this standard is to define a flexible system and apparatus capable of transporting video, audio and other data between a Source Device and a Sink Device over a digital communications interface.
FIG. 2 (Prior Art) and FIG. 3 (Prior Art) provide example block diagrams within the DP Standard to define the interface between a source device and a sink device. These diagrams appear on pages 26 and 141 of the DP Standard (Version 1.1) and are revised on page 48 of the DP Standard Errata.
FIG. 2 (Prior Art) is a block diagram for an embodiment 200 depicting a DP communication link 110 between a source device 102, such as an information handling system, and a sink device 104, such as a display device. As depicted, the source device 102 includes DP transmit (TX) circuitry 106, and the sink device 104 includes DP receive (RX) circuitry 108. The DP link 110 includes a main link 202, auxiliary channel 204 (AUX CH), and a Hot Plug Detect interrupt 206. The main link 202 is used to provide isochronous streams of data from the source device 102 to the sink device 104. The Hot Plug Detect interrupt 206 provides an interrupt signal from the sink device 104 to the source device 102. And the AUX CH 104 is a bi-directional signal line that is used to communicate link and device management information between the source device 102 and the sink device 104.
FIG. 3 (Prior Art) is a circuit diagram 300 for a connection circuit for the AUX CH 204 in FIG. 2 (prior art). As depicted, the AUX CH 204 is a differential connection including a positive signal line (AUX+) and a negative signal line (AUX−). The source device connector is indicated by dotted line 309, and the sink device connector is indicated by dotted line 307. The AUX CH connection is created by the physical connection of the source connector 309 to the sink connector 307.
For the source device, a differential transmit (TX) buffer 302 is coupled to the positive signal line (AUX+), and a differential receive (RX) buffer 304 is coupled to the negative signal line (AUX−). Two 50 ohm resistors are coupled in series between nodes 311 and 313. The common node between these two 50 ohm resistors is connected to a bias voltage (Vbias_TX). In addition, a 100 k ohm resistor is coupled between node 311 and ground. A 100 k ohm resistor is also coupled between node 313 and a positive voltage of about 2.5-3.3 volts. Further, an AC-coupling capacitor (C_AUX) is coupled between nodes 310 and 311, and an AC-coupling capacitor (C_AUX) is coupled between nodes 312 and 313.
For the sink device, a differential receive (RX) buffer 306 is coupled to the positive signal line (AUX+), and a differential transmit (TX) buffer 308 is connected to the negative signal line (AUX−). Two 50 ohm resistors are coupled in series nodes 315 and 317. The common node between these two 50 ohm resistors is connected to a bias voltage (Vbias_RX). In addition, a 1M ohm resistor is coupled between node 315 and a positive voltage of about 2.5-3.3 volts. A 1M ohm resistor is also coupled between node 317 and ground. Further, an AC-coupling capacitor (C_AUX) is coupled between nodes 314 and 315, and an AC-coupling capacitor (C_AUX) is coupled between nodes 316 and 317.
As described in the DP Standard Errata, the DP source device must weakly pull down the positive AUX+ signal line and weakly pull up the negative AUX− signal line with the 100 kΩ resistors between the AC-coupling capacitors (C_AUX) and the source connector 309 to assist detection by the sink device of a DP source device and a powered DP source device. The sink devices must very weakly pull up the positive AUX+ signal line and very weakly pull down the negative AUX− signal line with 1MΩ resistors between the sink connector 307 and the AC-coupling capacitors (C_AUX). As also set forth in the DP Standard Errata, when the DC voltage for the positive AUX+ signal line is at a low (L) level, a DP source device is connected. When the DC voltage for the negative AUX− signal line is at a high (H) level, a powered DP source device is connected. The following table summarizes the operation of the DP source detection as described in the DP Standard Errata.
TABLE 1(Prior Art)—Operation of Source Detectionas Set Forth in DP Standard andErrataAUX+ Signal LineAUX− Signal LineMeasurement by SinkMeasurement by SinkDeviceDeviceConclusionHIGHLOWSource DeviceDisconnectedLOWLOWSource DeviceConnected but NotPoweredLOWHIGHSource DeviceConnected andPowered
While the DP Standard and the DP Standard Errata describe a general technique for allowing a DP sink device to determine if a DP source device is connected and if this DP source device is powered, a more efficient solution is needed for determining if a DP source device is connected to a DP sink device.